As an information storage apparatus that stores and reads information by irradiating a dielectric with an electron beam, an apparatus using a cathode ray tube (CRT) similar to that for display had been studied much before core memories and semiconductor memories were put into practical use (for example, U.S. Pat. No. 2,755,994, column 2, lines 19 to 56.) In this patent, as in the case of displaying an image, a voltage of negative several thousand volts is applied to a red hot filament so as to emit thermoelectrons, and a dielectric (phosphor) is irradiated with an electron beam of the thermoelectrons, thereby storing and reading information.
More specifically, when a region of a dielectric associated with a storage bit is irradiated with a deflected electron beam, electron avalanche occurs in the irradiated region and electrons in the dielectric are emitted. In this state, the irradiated region becomes deficient in electrons. If the irradiation with the electron beam is stopped at this time, this electron deficiency state is maintained. On the other hand, if similar irradiation with an electron beam is performed from the region associated with the storage bit to its neighboring region according to scanning with the electron beam, electron avalanche also occurs in the neighboring region so that emitted electrons move to the region associated with the storage bit. At this time, the electron deficiency in the region associated with the storage bit is eliminated and the region changes into an indeficiency state. Then, this indeficiency state is maintained. That is, data “0” or “1” is stored by maintaining the electron deficiency or indeficiency state as described above.
As described above, when the region in the electron indeficiency state is irradiated with an electron beam and thereby changes into a deficiency state, the potential at a pickup plate provided on a tube face of a CRT varies depending on the change of the state. On the other hand, even when the region already in the deficiency state is irradiated with an electron beam, such a potential variation does not occur. Accordingly, stored data is read out by detecting a potential change (or current flowing due to the change) at the pickup plate.
—Problems to be Solved—
However, conventional information storage apparatuses as described above utilizing irradiation with electron beams have been replaced with core memories and then semiconductor memories, and are now not used at all because of the following reasons:
(1) The sizes of apparatuses themselves are large;
(2) Heaters and power supplies for the heaters are needed to emit thermoelectrons; and
(3) High voltages of about several thousand volts are required to emit electron beams.
On the other hand, the semiconductor memories currently used in general have their sizes greatly reduced and storage densities greatly increased, as compared to the information storage apparatuses utilizing irradiation with electron beams. However, semiconductor processes have constraints in fabrication, and therefore there arises the problem of difficulty in achieving a much higher density.
In view of this, it is therefore an object of the present invention to greatly increase the storage density so as to store a large amount of information.